Previously known presses of the above-mentioned type include a press that is constituted in a manner disclosed in Japanese Patent Application Laying-Open No. 2002-224889, for example. That is, a pressing member is slidably supported by a support to move up and down in order to press a workpiece, the pressing member being coupled through a crankshaft to a flywheel rotatably coupled to a motor, so that the pressing member is driven up and down by the rotational driving force of the motor through the flywheel and the crankshaft.
There is also another press that is constituted in a manner disclosed in Japanese Patent Application Laying-Open No. 8-174097. That is, an upper turret (which corresponds to a pressing member) slidably supported by a support to move up and down and including a punch for punching out a workpiece is driven up and down by a hydraulic cylinder, and a flywheel is attached to the driving shaft of an inclined plane variable capacity hydraulic pump that applies pressure to the hydraulic cylinder, which flywheel is driven by a motor via a belt.
Further, a press has been also known heretofore that utilizes a pneumatic cylinder as an alternative to the hydraulic cylinder.
In these known presses, the inertia of the flywheel is utilized to level out the fluctuations in the rotational speed of the motor, as well as to accumulate the rotational energy to carry out predetermined press works reliably. The motor for rotationally driving the heavy flywheel, however, generates very large noise and vibration, and thus being one of the causes of working environment deterioration.
Further, for the conventional press with a flywheel, the presence of the flywheel is a limiting factor for the reduction in size and weight of the press, and also causes a large loss of power since the flywheel is maintained to continuously rotate even when a press work is not performed. These problems become more serious in a large press that provides a large maximum pressing force.
In addition, in order to improve machining accuracy, it is desirable that the operation of a press, such as the operation speed thereof and the position and lifting stroke of a pressing member, being flexibly controlled in accordance with the goods to be manufactured, and that the machining condition of the press being always programmed optimally. The above mentioned conventional presses with flywheel, however, are difficult to operate so as to achieve high machining accuracy.